1. Field of the Invention
The invention is directed to a centrifuge and more particularly to a worm centrifuge for separating solids/liquid mixtures. Worm centrifuges generally comprise a rotatably seated drum jacket and a conveyor worm rotatable therein with a deviating speed. The drum includes liquid outlet openings arranged in the face wall of the centrifuge drum and solids discharge openings at the other end of the centrifuge drum. The conveyor worm directs the solids toward the solids discharge openings.
Solid bowl worm centrifuges have a means for the central delivery of the solids/liquid mixture to be separated into the centrifuge drum. The solid bowl worm centrifuges also include discharge openings for the discharge of the light and heavy substances separated from one another. In particular, a plurality of liquid outlet openings are provided in and distributed around the circumference of the face wall of the centrifuge drum for the discharge of the liquid freed of the solids, and the other (usually conically tapered) drum end likewise comprises discharge openings distributed around the circumference at its periphery through which the solids conveyed by the conveyor worm within the drum (and largely freed of the liquid) are discharged.
2. Description of the Prior Art
A prior art worm centrifuge is disclosed, for example, in German Published Application 40 33 070. FIG. 1 of that reference shows a liquid ring formed within the centrifuge drum during operation of such a worm centrifuge. The inside diameter of this liquid ring is determined by the radial arrangement of the liquid outlet openings uniformly distributed around the circumference of the drum or by the height of radially adjustable weir plates. The weir plates permit adjustment of the liquid level or the pool depth. When shutting the worm centrifuge off (the shut-down process), the speed of the centrifuge drum diminishes until the centrifuge achieves a standstill and the centrifugal force thus also diminishes or is reduced during the shut-down process. Upon shut-down of the centrifuge drum, the drum reaches a speed at which the centrifugal force is lower than the force of gravity, and this results in the liquid ring within the centrifuge drum collapsing so that the filling level of the liquid within the centrifuge drum extends beyond the solids discharge openings. This causes the liquid to undesirably discharge--though only briefly--in a wave-like fashion at the solids discharge openings.
German Published Application 40 33 070 proposes that the weir plates of the liquid outlet openings can be adjusted radially outward during the shut-down process in order to reduce the pool depth of the liquid ring as quickly as possible. However, a substantial residual quantity of liquid still remains in the centrifuge drum. In particular, the liquid ring that has remained at the inside wall of the drum suddenly collapses before the operating standstill, and this residual quantity of liquid can undesirably depart the drum at the solids discharge side. Conversely, the liquid remaining in the centrifuge drum can, upon restart of the worm centrifuge, increase the mass moment of inertia of the rotor and thus make start-up and acceleration of the masses within the centrifuge more difficult.
One object of the invention is therefore to avoid these disadvantages of the prior art and provide a worm centrifuge that overcomes the problems during the start-up process and shut-down process that derive from the quantity of liquid situated in or remaining in the centrifuge drum. Particularly, one object of the invention is to overcome the problem of liquid discharging through the solids discharge openings during the shut-down process.